Two liquids with different densities can be separated from each other by means of a centrifugal separator. Alternatively or additionally, a centrifugal separator can be used for separating sludge and/or other solids from a liquid. For example, centrifugal separators in connection with piston engines in marine or power plant use are used for separating sludge and water from lubrication oil and fuel. A centrifugal separator typically comprises a rotatable bowl, i.e. a rotor, having a stack of disks. A sludge volume for the heavier liquid and the sludge or solids is formed inside the bowl adjacent to the perimeter of the bowl. As the bowl rotates, the solids and/or the heavier liquid, i.e. the liquid having a higher density, are transferred by centrifugal force into the sludge volume of the bowl, from which they can be removed. The separated liquid, having a lower density, is transferred through the disk stack to the inner part of the bowl, wherefrom it is discharged from the separator.
The heavier material is discharged from the bowl via discharge openings at certain intervals. The discharge openings are usually opened and closed hydraulically. In a typical centrifugal separator, the bowl comprises a lower half and an upper half. The lower half is pressed against the upper half by hydraulic pressure in a closure chamber. By introducing control liquid into a control chamber, the hydraulic pressure can be discharged from the closure chamber. The lower half is thus displaced and the discharge openings are revealed. At the end of a discharge event, closure liquid is introduced into the closure chamber and the lower half moves upwards covering the discharge openings and ending the discharge event. The closure liquid and the control liquid are typically fresh water. At power plants, the separators are usually connected to the same fresh water system as many other consumers of fresh water, such as a steam system and equipment for turbocharger washing. If equipment connected to the fresh water system is using a lot of water, the separators may suffer from lack of water or of reduced water pressure. If a scheduled discharge event takes place at such a point of time, the discharge openings may not open or do not close properly.